title: Ocular response analyser to assess hysteresis and corneal resistance factor in low tension, open angle glaucoma and ocular hypertension.
abstract: OBJECTIVE
  The aim of this study is to compare the hysteresis and corneal resistance factor (CRF) in normal tension glaucoma (NTG), primary open angle glaucoma (POAG) and ocular hypertension (OHT) eyes measured by the ocular response analyser (ORA).
  
  
  METHODS
  This is a prospective, cross-sectional and comparative clinical trial. The setting was a teaching hospital in Birmingham, England.
  
  
  METHODS
  216 eyes with POAG, 68 eyes with NTG and 199 eyes with OHT. Observational procedures: Goldmann applanation tonometry and intraocular pressure (IOP), hysteresis and CRF measured by ORA and central corneal thickness (CCT) by ultrasonic pachymetery. The main outcome measures were IOP, CCT, hysteresis and CRF.
  
  
  RESULTS
  The hysteresis in NTG, POAG and OHT eyes was 9.0 +/- 1.9, 9.9 +/- 2.1 and 10.2 +/- 2.0 mmHg; CRF was 9.1 +/- 2.2, 10.6 +/- 2.0 and 12.0 +/- 2.0 mmHg; IOP by Goldmann applanation tonometry and ORA was 14.7 +/- 2.8 and 15.3 +/- 4.2 mmHg, 16.7 +/- 4.0 and 16.9 +/- 4.6 mmHg and 20.5 +/- 4.1 and 20.0 +/- 4.5 mmHg; CCT was 526.5 +/- 42.2, 537.0 +/- 36.0 and 563.4 +/- 35.9 microm, respectively. The difference for CRF, IOP and CCT for NTG, POAG and OHT eyes was statistically significant.
  
  
  CONCLUSIONS
  Hysteresis and CRF were highest in OHT eyes. These factors may prove to be useful measurements of ocular rigidity and may help to understand role of the corneal rigidity in monitoring the progress of conditions such as NTG, POAG and OHT.
authors.affiliation: Heart of England Foundation Trust, Solihull, UK.
authors.forename: Sunil
authors.initials: S
authors.lastname: Shah
authors.forename: Mohammad
authors.initials: M
authors.lastname: Laiquzzaman
authors.forename: Sanjay
authors.initials: S
authors.lastname: Mantry
authors.forename: Ian
authors.initials: I
authors.lastname: Cunliffe
mesh_terms: D003315:Cornea / Q000000981:diagnostic imaging; D003430:Cross-Sectional Studies; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D004548:Elasticity; D005901:Glaucoma / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005902:Glaucoma, Open-Angle / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure; D009798:Ocular Hypertension / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011446:Prospective Studies; D014065:Tonometry, Ocular; D014463:Ultrasonography; D014783:Viscosity